design, synthesis, and characterization of polymeric materials for uses in energy storage applications

The Pennsylvania State University The Graduate School Department of Chemistry DESIGN, SYNTHESIS, AND CHARACTERIZATION OF POLYMERIC MATERIALS FOR USES IN ENERGY STORAGE APPLICATIONS A Thesis in Chemistry by Daniel Thomas Welna © 2006 Daniel Thomas Welna Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy August 2006 UMI Number: 3231914 3231914 2006 UMI Microform Copyright All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, MI 48106-1346 by ProQuest Information and Learning Company. The thesis of Daniel Thomas Welna was reviewed and approved* by the following: Harry R. Allcock Evan Pugh Professor of Chemistry Thesis Advisor Chair of Committee Karl T. Mueller Associate Professor of Chemistry Alan J. Benesi Lecturer in Chemistry James P. Runt Professor of Polymer Science Associate Head for Graduate Studies Ayusman Sen Professor of Chemistry Head of the Department of Chemistry *Signatures are on file in the Graduate School iii ABSTRACT The work described in this thesis focuses on the design, synthesis, and characterization of polymeric materials for energy storage applications, which include small molecule electrolyte additives, solid polymer electrolyte, and gel polymer electrolyte systems. In addition, non-woven nanofiberous mats of a pre-ceramic polymer were examined for high-strength and temperature material applications. Chapter 2 of this thesis describes the synthesis of novel polyphosphazene single ion conductors for use in secondary lithium ion batteries. Chapters 3 and 4 details work towards the synthesis and evaluation of highly selective membranes for use in lithium-seawater batteries. The fifth chapter deals with the synthesis and characterization of a polyphosphazene-silicate solid polymer electrolyte networks for secondary lithium batteries. Chapter 6 describes the fabrications and evaluation a gel polymer electrolyte system which utilizes a phosphate- based small molecule electrolyte additive. The appendix details the electrostatic spinning of a polymeric ceramic precursor to produce a nanofiberous mat, which upon pyrolysis yield boron carbide nanofibers. Chapter 2 describes the synthesis and characterization of novel single ion conductive polymer electrolytes developed by covalently linking an arylsulfonimide substituent to the polyphosphazene backbone. An immobilized sulfonimide lithium salt is the source of lithium cations, while a cation-solvating cosubstituent, 2-(2- methoxyethoxy)ethoxy, was used to increase free volume and assist cation transport. The ionic conductivities showed a dependence on the percentage of lithiated sulfonimide substituent present. Increasing amounts of the lithium sulfonimide component increased iv the charge carrier concentration but decreased the ionic conductivity due to decreased macromolecular motion and possible increased shielding of the nitrogen atoms in the polyphosphazene backbone. The ion conduction process was investigated through model polymers that contained the non-immobilized sulfonimide – systems that had higher conductivities than their single ion counterparts. Chapter 3 details the synthesis of novel polyoctenamers with pendent functionalized-cyclotriphosphazenes as amphiphilic lithium-ion conductive membranes. Cyclotriphosphazene monomers were functionalized with one cycloocteneoxy substituent per ring. Two different types of monomer units, one with oligoethyleneoxy cation- coordination side groups and the other with hydrophobic fluoroalkoxy side groups, were then prepared. The syntheses of these monomers, their ring-opening metathesis copolymerization, and the characteristics of the resultant polymers are discussed, with an emphasis on the dependence of ionic conductivity and hydrophobicity on polymer composition. Chapter 4 focuses the design of novel amphiphilic single-ion conductive polynorbornenes with pendent cyclotriphosphazenes as candidates for lithium-ion conductive membranes for lithium-seawater batteries. The cyclotriphosphazene components were linked to a 5-norbornene-2-methoxy substituent to provide a polymerizable unit. 2-(2-Phenoxyethoxy)ethoxy co-substituents on the cyclotriphosphazene unit of the first co-monomer were utilized to simultaneously facilitate lithium cation transport and introduce hydrophobicity into the polymer electrolyte. 4-(Lithium carboxalato)phenoxy side groups were linked to the rings of a second co-monomer to provide tethered anions with mobile lithium cations and to v increase the dimensional stability of the final polymers. The synthesis of norbornenemethoxy-based cyclotriphosphazene monomers, their ring-opening metathesis polymerization, deprotection and lithiation of the 4-(propylcarboxalato)phenoxy side groups, and the characterization of the polymers are discussed to illustrate the dependence of ion transport and hydrophobic properties on the polymer composition. Chapter 5 is an analysis of the ionic conduction characteristics of silicate sol-gel poly[bis(methoxyethoxyethoxy)phosphazene] hybrid networks synthesized by hydrolysis and condensation reactions. Conversion of the precursor polymers to covalently interconnected hybrid networks with controlled morphologies and physical properties was achieved. Thermal analyses showed no melting transitions for the networks and low glass transition temperatures that ranged from approximately -38 °C to -67 °C. Solid solutions with lithium bis(trifluoromethanesulfonyl)amide in the network showed a maximum ionic conductivity value of 7.69 × 10 -5 S/cm, making these materials interesting candidates for dimensionally stable solid polymer electrolytes. Chapter 6 investigates the influence of an organophosphate electrolyte additive on poly(ethylene oxide) lithium bis(trifluoromethylsulfonyl)imide-based gel polymer electrolytes for secondary lithium battery applications. Tris(2-(2- methoxyethoxy)ethyl)phosphate, is compared to the well known gel-battery component, propylene carbonate, through a study of complex impedance analysis, differential scanning calorimetry, and limiting oxygen index combustion analysis. The conductivities of the gels at low concentrations of tris(2-(2-methoxyethoxy)ethyl)phosphate (1.9 - 4.2 mol %) are higher to those of propylene carbonate based systems with the same concentration. Despite micro-phase separation at high concentrations of tris(2-(2- vi methoxyethoxy)ethyl)phosphate (7.0 – 14.9 mol %), the conductivities remain comparable to systems that use propylene carbonate. The addition of tris(2-(2- methoxyethoxy)ethyl)phosphate to poly(ethylene oxide) gives increased fire retardancy, while the addition of propylene carbonate to poly(ethylene oxide) results in increased flammability. The appendix is a pyrolysis study of electrostatically spun poly(norbornenyldecaborane), a polymeric boron carbide precursor. Electrostatic spinning techniques provided an efficient and large scale route to non-woven mats of boron-carbide/carbon nanoscale ceramic fibers with narrow size distributions. Scanning electron microscopy, x-ray diffraction analysis and diffuse reflectance infrared Fourier transform spectroscopy were used to characterize the polymer and ceramic fibers. The results suggest that electrostatic spinning followed by pyrolysis can be used as a general route to a wide variety of single-phase and hybrid non-oxide ceramic fibers. vii TABLE OF CONTENTS LIST OF FIGURES xi LIST OF TABLES xv PREFACE xvi ACKNOWLEDGEMENTS xvii 1.1 Polymeric materials 1 1.1.1 History of polymer chemistry 2 1.1.2 Polymer architecture 3 1.1.3 Polymerization type 7 1.1.3.1 Step-growth polymerization 8 1.1.3.2 Chain-growth polymerization 11 1.1.3.3 Ring-opening polymerization 14 1.1.4 Polymer composition 17 1.1.4.1 Organic polymers 17 1.1.4.2 Inorganic polymers 19 1.1.4.3 Hybrid inorganic-organic polymers 19 1.2 Polyphosphazenes 20 1.2.1 History of polyphosphazenes 22 1.2.2 Polyphosphazene architecture 23 1.2.3 Synthesis of polyphosphazenes 25 1.2.3.1 Thermal ring-opening polymerization 25 1.2.3.2 Alternative polymerization methods 29 1.2.3.3 Macromolecular substitution 30 1.2.4 General structure-property relationships 31 1.2.5 Applications 34 1.3 Polymer electrolytes 38 1.3.1 History 43 1.3.2 Types of polymeric electrolytes 45 1.3.3 Mechanisms of ion transport 50 1.3.4 Phosphazene polymer electrolytes 50 1.4 References 53 Chapter 2 Single ion conductors - polyphosphazenes with sulfonimide functional groups 62 2.1 Introduction 62 2.2 Experimental 64 2.2.1 Materials 64 2.2.2 Equipment 65 viii 2.2.3 Synthesis of [NP((OCH 2 CH 2 ) 2 OCH 3 ) x (OC 6 H 4 SO 2 N(Li)SO 2 CF 3 ) y ] n (2-5) 66 2.2.4 Synthesis of [NP((OCH 2 CH 2 ) 2 OCH 3 ) x (OC 6 H 5 ) y ] n (8-11) 68 2.2.5 Preparation of solid polymer electrolytes 69 2.2.6 Preparation of gel polymer electrolytes 69 2.3 Results and discussion 70 2.3.1 Synthesis of [NP((OCH 2 CH 2 ) 2 OCH 3 ) x (OC 6 H 4 SO 2 N(Li)SO 2 CF 3 ) y ] n (2-5) 70 2.3.3 Ionic conductivity as a function of T g and E a 76 2.3.4 Mechanism of ionic conductivity 82 2.3.5 Gel polymer electrolytes of polymer 4 with N-methyl-2- pyrrolidinone 86 2.4 Conclusions 88 2.5 References 89 Chapter 3 Synthesis of pendent functionalized-cyclotriphosphazenes polyoctenamers: hydrophobic lithium-ion conductive materials 91 3.1 Introduction 91 3.2 Experimental 95 3.2.1 General 95 3.2.2 Materials 96 3.2.3 Preparation of cyclotriphosphazene-functionalized monomers 97 3.2.4 General procedure for ring-opening metathesis polymerization 100 3.2.5 Preparation of solid polymer electrolytes 104 3.2.6 Preparation of films for static water contact angle measurements 105 3.3 Results and discussion 105 3.3.1 Monomer synthesis 105 3.3.2 Polymer synthesis 107 3.3.3 Polymer characterization 110 3.3.4 Thermal analysis 111 3.3.5 Ionic conductivity and hydrophobicity 114 3.4 Conclusions 119 3.5 References 121 Chapter 4 Lithium-ion conductive polymers as prospective membranes for lithium-seawater batteries 124 4.1 Introduction 124 4.2 Experimental 132 4.2.1 Materials 132 4.2.2 Equipment 133 4.2.3 Synthesis of 2-(2-phenoxyethoxy)ethanol (2) 134 4.2.4 Synthesis of 5-norbornene-2-methoxy- pentakis(chloro)cyclotriphosphazene (monomer 3) 135 ix 4.2.5 Synthesis of 5-norbornene-2-methoxy-pentakis(2-(2- phenoxyethoxy)ethoxy)cyclotriphosphazene (monomer 4) 136 4.2.6 Synthesis of 5-norbornene-2-methoxy-pentakis(4- propylcarboxalatophenoxy)cyclotriphosphazene (monomer 5) 137 4.2.7 Procedure for ring-opening metathesis polymerization 137 4.2.8 General procedure for deprotection and lithiation of polymers 6-9 139 4.2.9 Preparation of polymer electrolyte samples for impedance analysis 140 4.2.10 Preparation of films for static water contact angle measurements 141 4.3 Results and Discussion 141 4.3.1 Synthesis of monomers 141 4.3.2 Synthesis of polymers 144 4.3.3 Polymer characterization 145 4.3.4 Solid polymer electrolytes - morphological properties 146 4.3.5 Solid polymer electrolytes - temperature-dependent ionic conductivity 146 4.3.6 Solid polymer electrolytes - hydrophobic properties 151 4.4 Conclusions 152 4.5 References 153 Chapter 5 Ionic conductivity of covalently interconnected polyphosphazene- silicate hybrid networks 155 5.1 Introduction 155 5.2.1 Materials 159 5.2.2 Equipment 159 5.2.3 Synthesis of polyphosphazene-silicate hybrid networks 162 5.3 Results and discussion 163 5.3.1 Network synthesis 163 5.3.2 Thermal analysis 164 5.3.3 Ionic conductivity analysis 166 5.4 Conclusions 169 5.5 References 170 Chapter 6 A phosphate additive for poly(ethylene oxide)-based gel polymer electrolytes 172 6.1 Introduction 172 6.2 Experimental 174 6.2.1 Materials 174 6.2.2 Equipment 177 6.2.3 Synthesis of tris(2-(2-methoxyethoxy)ethyl)phosphate (1) 178 6.2.4 Preparation of gel polymer electrolyte samples 178 6.3 Results and discussion 180 6.3.1 Ionic conductivity analysis 180 6.3.2 Thermal transition analysis 185 [...]... architectures 5 Linear polymers have the simplest type of architecture and are generally soluble in many organic solvents Additionally, the linear architecture allows for the polymer chains to become closely packed together favoring the formation of crystalline regions A branched polymer contains branching sites along the polymer chain, which disrupts the ability of the chains to closely pack together and form... polystyrene, and polycarbonate.1 Then in the late 20th century the field of polymer chemistry began to take its attention off of exploiting previously commercialized polymers and refocused its efforts on developing new polymers for high-performance applications. 2 Next generation batteries, fuel cells, visual displays, drug delivery platforms, and fire retardants are only a few of the applications where new polymeric. .. structure of the monomer units plays an integral role in determining the physical properties of the polymer, the architecture of the polymer chain can have an equeally important impact There are five general types of polymer architectures and they include linear, branched, star, dendrimer, and cross-linked (Figure 1-1).2,10,11 4 Linear Branched Star Dendrimer Cross-linked Figure 1-1: Types of polymer... Allcock and A.M Maher Chapter 3 has been adapted for publication in Macromolecules and was coauthored by H.R Allcock and D.A Stone Chapter 4 has been adapted for publication in Chemistry of Materials and was coauthored by H.R Allcock and D.A Stone Chapter 5 has been adapted for publication in Solid State Ionics and was coauthored by H.R Allcock and Y Chang Chapter 6 has been adapted for publication in Solid... This process can be described in three key steps: initiation, propagation, and termination The initiation step requires the activation of a monomer from which the polymer chain will grow The next step involves the propagation of the active chain end with additional monomers causing the chain to increase in length Termination is when the active chain end is quenched, making it unable to grow any longer... Ionics and was coauthored by H.R Allcock, R.M Morford, C.E Kellam III, and M.A Hoffmann The appendix was adapted for publication in Advanced Materials and was coauthored by H.R Allcock, L.G Sneddon, J.D Bender, and X Wei xvii ACKNOWLEDGEMENTS I would like to thank my advisor, Professor Harry R Allcock, for giving me the opportunity to join his research program and for his constant support and guidance... commonly occurs during chain-growth polymerizations is chain transfer This happens when the active site on a chain end is transferred to another polymer chain or free monomer, as opposed to monomer at the end of the growing polymer chain Upon transfer of the active site to another polymer chain, branching sites can arise causing a change in the morphology of the final polymer On the other hand, if the active... Random and alternating copolymers typically exhibit properties that are intermediate of the two respective homopolymers of each monomer The third type of copolymer architecture is a block copolymer This type of architecture contains a polymer of one monomer linearly linked to a polymer of a different monomer Graft copolymers result when there is a central polymer chain that has branching points to... monomers into linear polymer chains (Figure 1-6).2,10,13 ROP is a type of chain polymerization that consists of the initiation, propagation, and termination steps However, unlike the typical chain polymerizations of carbon-carbon double-bond monomers, the propagation rate constants are similar to those in step-growth polymerizations, which lead to a slow rate of molecular weight increase The ability of a... The ability of a cyclic monomer to be initiated and undergo chain propagation is primarily governed by thermodynamics, having to do with the relative stabilities of the cyclic monomer (ring-strain) and linear polymer structure Typical initiation in ROP occurs via cationic or anionic means by the use of ionic initiators Some inorganic polymers like polysiloxanes and polyphosphazenes also are synthesized . Graduate School Department of Chemistry DESIGN, SYNTHESIS, AND CHARACTERIZATION OF POLYMERIC MATERIALS FOR USES IN ENERGY STORAGE APPLICATIONS A Thesis in Chemistry by Daniel. design, synthesis, and characterization of polymeric materials for energy storage applications, which include small molecule electrolyte additives, solid polymer electrolyte, and gel polymer electrolyte. conductivity value of 7.69 × 10 -5 S/cm, making these materials interesting candidates for dimensionally stable solid polymer electrolytes. Chapter 6 investigates the influence of an organophosphate